JP5078701B2 - Liquid crystal optical element and optical pickup device - Google Patents

Description

  The present invention relates to a liquid crystal optical element and an optical pickup device, and more particularly to a liquid crystal optical element that diffracts a light beam and an optical pickup device having such a liquid crystal optical element.

  A reflected beam reflected from the optical recording medium is split by a beam splitting element and incident on a photodetector, and an FE (focus error) signal is generated by using the 0th order light and the primary light of the light incident on the beam splitting element. And obtaining a TE (tracking error) signal (for example, Patent Document 1).

  Japanese Patent Laid-Open No. 2004-228561 has three types of regions instead of the beam splitting element, transmits most of the incident beam to generate zero-order light, and transmits a part of the light amount to provide three types. It is described that a beam splitting element that generates primary light from each of these areas can be used, and another photodetector corresponding to the beam splitting element can be used. Note that the beam splitting element described in Patent Document 1 is a diffraction grating in which a plurality of grooves are actually formed, and is arranged and fixed in the optical path of the light beam.

  By the way, in an optical pickup device that combines writing or reading on a CD or general DVD and writing or reading on a Blu-ray DVD, a red beam (660 nm) for a CD or general DVD is utilized using the same optical path. And a blue beam (405 nm) for a Blu-ray DVD. In such a case, it is necessary to provide a photodetector that is applied to each light beam. Therefore, a beam splitting element for irradiating with a plurality of beams divided to each photodetector also corresponds to each light beam. I had to set up.

  However, for this purpose, it is necessary to provide a mechanism for taking a plurality of beam splitting elements into and out of the beam optical path, and there are problems such as an increase in cost and a reduction in size of the apparatus.

JP 2004-281026 A (FIGS. 12, 13, 18, and 19)

  Accordingly, an object of the present invention is to provide a liquid crystal optical element and an optical pickup device aimed at solving the above-mentioned problems.

  It is another object of the present invention to provide a liquid crystal optical element that functions reliably as a diffraction element and an optical pickup device using such a liquid crystal optical element.

  Furthermore, the present invention provides a liquid crystal optical element that can be used as a diffractive element and a non-diffractive element with the use of a light beam having a plurality of wavelengths, and an optical pickup device using such a liquid crystal optical element. The purpose is to do.

  In order to solve the above-described problems, a liquid crystal optical element according to the present invention includes a liquid crystal layer sandwiched between a pair of transparent substrates, a transparent layer disposed on one transparent substrate of the pair of transparent substrates and having a diffraction pattern. A liquid crystal panel having an electrode and a transparent counter electrode disposed on the other transparent substrate of the pair of transparent substrates, and generating a potential difference between the transparent electrode and the transparent counter electrode to position the liquid crystal layer A driving unit that causes the liquid crystal panel to function as a diffractive element that generates a phase difference distribution and diffracts a transmitted backward light beam, and the driving unit divides the diffraction pattern into a plurality of regions or a plurality of the transparent counter electrodes; In other words, the potential difference is adjusted for each region.

  In order to solve the above problems, an optical pickup device according to the present application includes a light source that emits a light beam, a liquid crystal layer sandwiched between a pair of transparent substrates, and one transparent substrate on the pair of transparent substrates. And a transparent electrode having a diffraction pattern and a liquid crystal panel having a transparent counter electrode disposed on the other transparent substrate of the pair of transparent substrates, and a potential difference between the transparent electrode and the transparent counter electrode. Generating a phase difference distribution in the liquid crystal layer and generating a diffracted light diffracted by the liquid crystal panel; A light detection unit that receives light, and the driving unit divides the diffraction pattern into a plurality of regions or divides the transparent counter electrode into a plurality of regions, and adjusts a potential difference for each region. It is characterized in.

  Furthermore, in order to solve the above problems, an optical pickup device according to the present application is sandwiched between a first light source that emits a first light beam, a second light source that emits a second light beam, and a pair of transparent substrates. A liquid crystal panel having a liquid crystal layer, a transparent electrode disposed on one transparent substrate of the pair of transparent substrates and having a diffraction pattern, and a transparent counter electrode disposed on the other transparent substrate of the pair of transparent substrates A liquid crystal optical element having a drive unit that generates a potential difference between the transparent electrode and the transparent counter electrode, and when the first light beam is emitted from the first light source, the drive unit is applied to the liquid crystal panel. The liquid crystal layer functions as a diffractive element that diffracts the return light beam of the first light beam that is transmitted by generating a phase difference distribution, and the driving is performed when the second light beam is emitted from the second light source. A switching unit that switches the liquid crystal layer to function as a non-diffractive element, and a light detection unit that receives the diffracted light diffracted by the liquid crystal panel when the first light beam is emitted from the first light source. The drive unit divides the diffraction pattern into a plurality of regions or divides the transparent counter electrode into a plurality of regions, and adjusts a potential difference for each region.

  According to the present invention, it is possible to reduce the cost and size of the optical pickup device by using the liquid crystal panel as a diffraction element.

  In addition, according to the present invention, the liquid crystal panel can be controlled so as to obtain diffracted light similar to that of a diffraction grating in which grooves are physically formed.

  Furthermore, according to the present invention, the liquid crystal panel can be switched and used as a diffraction grating when a high-density optical recording medium is used, and as a non-diffractive element when a CD or DVD is used. It was.

  A liquid crystal optical element and an optical pickup device according to the present invention will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a diagram showing a schematic configuration of an optical pickup device according to the present invention.

  FIG. 1 shows a case where reproduction from a high-density optical recording medium 60 such as a Blu-ray disc is performed. In that case, in the optical pickup device 10, the 405 nm wavelength blue laser light emitted from the first light source 11, which is a semiconductor laser, is converted into substantially parallel light by the first collimating lens 12, and the half mirror 13 and the polarization beam splitter 14 are converted. And enters the λ / 4 plate 15. The light beam (outgoing light) converted from linearly polarized light to circularly polarized light by the λ / 4 plate 15 is condensed on the high-density optical recording medium 60 (in this case, a Blu-ray disc) by the objective lens 16.

  The reflected light from the high-density optical recording medium 60 passes through the objective lens 16 again, passes through the λ / 4 plate 15, and is converted from circularly polarized light into linearly polarized light whose polarization direction is orthogonal to the forward light. The light beam emitted from the λ / 4 plate 15 is reflected by the polarization beam splitter 14 and enters the liquid crystal panel 30.

  Here, as will be described later, the liquid crystal panel 30 generates a predetermined phase difference distribution by generating a predetermined potential difference between the transparent electrode having the diffraction pattern and the transparent counter electrode 32 by the liquid crystal driving unit 40. However, it is configured to function as a diffraction element. Therefore, the light beam incident on the liquid crystal panel 30 is diffracted into one zero-order diffracted light and three first-order diffracted lights, and is condensed onto the photodetector 50 by the condenser lens 41.

  The photodetector 50 outputs an FE (focus error) signal, a TE (track error) signal, and an RF signal based on the collected diffracted light. In a control mechanism (not shown), the driving mechanism 17 is controlled using the FE signal and the TE signal output from the light detector 50, the objective lens 16 is focused and tracked, and a predetermined density on the high-density optical recording medium 60 is determined. The position is controlled so that the focused spot by the objective lens 16 always follows. A control mechanism (not shown) reproduces information recorded on the high-density optical recording medium 60 based on the RF signal output from the photodetector 50.

  When information is written to the high-density optical recording medium 60, the emission of the light beam from the first light source 11 is modulated according to the recording information, and the FE signal and TE output from the photodetector 50 are modulated. Information is written by decomposing, deforming or altering the dye of the writable high-density optical recording medium 60 by the thermal action of the laser beam while tracking and focusing the objective lens 16 using the signal.

  When reproducing information from a low- or medium-density optical recording medium such as a CD or DVD in the optical pickup device 10 shown in FIG. 1, a red laser with a wavelength of 660 nm emitted from the second light source 21 that is a semiconductor laser. The light is converted into substantially parallel light by the second collimating lens 22 and divided into three beams by the diffraction element 23. The three beams divided by the diffraction element 23 are reflected by the half mirror 13, pass through the polarization beam splitter 14, and enter the λ / 4 plate 15. Three beams (outgoing light) converted from linearly polarized light to circularly polarized light by the λ / 4 plate 15 are condensed on a CD or DVD (not shown) by the objective lens 16.

  The diffraction element 23 is actually a diffraction grating in which a plurality of grooves are formed, and is disposed and fixed in the optical path of the light beam. However, similarly to the liquid crystal panel 30, the liquid crystal layer may be used.

  The three beams reflected from the CD or DVD pass through the objective lens 16 again, pass through the λ / 4 plate 15, and are converted from circularly polarized light to linearly polarized light whose polarization direction is orthogonal to the forward light. The three beams emitted from the λ / 4 plate 15 are reflected by the polarization beam splitter 14 and enter the liquid crystal panel 30.

  Here, as will be described later, the liquid crystal panel 30 is configured to function as a non-diffractive element. Accordingly, the three beams incident on the liquid crystal panel 30 pass through the liquid crystal panel as they are, and are condensed on the photodetector 50 by the condenser lens 41.

  The photodetector 50 outputs an FE (focus error) signal, a TE (track error) signal, and an RF signal based on the collected three beams. In a control mechanism (not shown), the drive mechanism 17 is controlled using the FE signal and TE signal output from the photodetector 50, the objective lens 16 is focused and tracked, and a predetermined position on the CD or DVD is objectively detected. Control is performed so that the focused spot by the lens 16 always follows. A control mechanism (not shown) reproduces information recorded on the CD or DVD based on the RF signal output from the photodetector 50.

  When writing information to a low- or medium-density optical recording medium such as a CD or DVD, the light beam emitted from the second light source 21 is modulated in accordance with the recording information and output from the photodetector 50. Information is written by decomposing, deforming or altering the writeable CD or DVD dye by the thermal action of the laser beam while tracking and focusing the objective lens 16 using the FE signal and TE signal. I do.

  FIG. 2 is a diagram showing the photodetector 50 when the high-density optical recording medium 60 is used.

  The photodetector 50 has a total of 20 light receiving parts 50a to 50t. In this case, the light receiving parts 50i to 50l receive the 0th-order diffracted light 80, the light receiving parts 50m to 50p receive the first first-order diffracted light 81, the light receiving parts 50q to 50t receive the second first-order diffracted light 82, and the light receiving part 50e. ˜50 h are arranged to receive the third first-order diffracted light 83. Each of the light receiving units 50a to 50t is configured to output current values I50a to I50t, respectively, according to the received light.

  For example, the FE signal can be obtained by the calculation of (I50i + I50k) − (I50j + I50l). Further, the TE signal can be obtained by calculation of (I50q + I50r) − (I50s + I50t). Further, the spherical aberration error signal can be obtained by calculation of (I50m + I50o) − (I50n + I50p) −C × {(I50e + I50g + I50q + I50s) − (I50f + I50h + I50r + I50t)}. Here, C is a constant. Further, the RF signal can be obtained by calculation of I50i + I50j + I50k + I50l. Note that the above arithmetic expression is an example, and other arithmetic expressions can be used.

  FIG. 3 is a diagram showing the photodetector 50 when a CD or a DVD is used.

  In this case, the photodetector 50 receives the beam divided into three by the diffractive element 23, the light receiving units 50a to 50d receive the −1st order light 84, and the light receiving units 50i to 50l receive the 0th order light 85. The light receiving portions 50m to 50p are arranged so as to receive the −1st order light 86.

  For example, the FE signal can be obtained by the calculation of (I50i + I50k) − (I50j + I50l). The TE signal can be obtained by the calculation of [(I50i + I50j) − (I50k + I50l)] − C [(I50a + I50b + I50m + I50n) − (I50c + I50d + I50o + I50p)]. Here, C is a constant. Further, the RF signal can be obtained by calculation of I50i + I50j + I50k + I50l. Note that the above arithmetic expression is an example, and other arithmetic expressions can be used.

  FIG. 4 is a diagram for explaining a method of driving the liquid crystal panel.

  The liquid crystal panel 30 is connected to a power supply unit 70 and a control unit 71 configured by a CPU, ROM, RAM, and the like, and is driven by a liquid crystal drive unit 40 configured by an IC or the like. Based on the control signal from the control unit 71, the liquid crystal driving unit 40 adjusts the light amount of the liquid crystal panel 30, and performs switching control according to the recording medium (for high-density recording medium 60 and for CD or DVD), ON / OFF Control and so on. In the present application, a combination of the liquid crystal panel 30 and the liquid crystal driving unit 40 is referred to as a liquid crystal optical element 45.

  FIG. 5 is a schematic sectional view of the liquid crystal panel 30.

  The liquid crystal panel 30 includes a first transparent substrate 31, a second transparent substrate 36, a sealing member 39, a plurality of spacers 38 arranged to maintain a distance between the first and second transparent substrates 31 and 36, a first and a second. A liquid crystal layer 37 and the like sealed between the transparent substrates 31 and 36 and the seal member 39 are included. A transparent counter electrode (solid electrode) 32 and a first alignment film 33 are formed on the first transparent substrate 31, and a transparent electrode 100 and a second alignment film 34 are formed on the second transparent substrate 36. . It should be noted that the scale may differ from the actual for the sake of explanation. For the liquid crystal layer 37, nematic liquid crystal or the like subjected to homogeneous alignment or homeotropic alignment treatment is used.

  The first and second transparent substrates 31 and 36 are flexible and are formed of polycarbonate resin having a thickness of 100 μm. However, the first and second transparent substrates 31 and 36 may be a transparent glass substrate, a modified acrylic resin, a polymethacrylic resin, a polyether sulfone resin, a polyethylene terephthalate resin, a norboltene resin, and the thickness is 50 μm to It can be 250 μm.

  The transparent counter electrode 32 and the transparent electrode 100 are formed by vapor-depositing a transparent conductive film made of ITO having a thickness of about 0.03 μm on the first and second transparent substrates 31 and 36, respectively, and thereafter Unnecessary portions are removed by etching.

  FIG. 6 is a diagram illustrating an example of a transparent electrode.

  As shown in FIG. 6, the transparent electrode 100 of the liquid crystal panel 30 has three types of regions, and the effective diameter of the light beam reflected by the polarizing beam splitter 14 is the outer shape of the transparent electrode 100 shown in FIG. It is comprised so that it may become substantially the same shape. In FIG. 6, arrows indicate the alignment directions of the first alignment film 33 and the second alignment film 34 of the liquid crystal panel 30.

  The first region 101 of the transparent electrode 100 is a substantially circular region corresponding to the central portion of the light beam, and has a predetermined width arranged in the same direction as the alignment direction A at a pitch s1 (for example, 10 μm). A diffraction pattern composed of a strip-shaped pattern is formed. Further, the second region 102 of the transparent electrode 100 has a diffraction pattern composed of a strip-like pattern having a predetermined width and arranged in the same direction as the alignment direction A at a pitch s2 (for example, 5 μm) (s2 <s1). Is formed. Further, the third region 103 of the transparent electrode 100 is formed with a diffraction pattern composed of a strip-like pattern having a predetermined width and arranged in a direction substantially orthogonal to the alignment direction A at a pitch s1.

  When the high-density optical recording medium 60 is used, a predetermined phase difference distribution is generated in the liquid crystal panel 30 by the liquid crystal driving unit 40, and thus functions as a diffraction element. In that case, the light transmitted through the entire transparent electrode 100 is detected as the 0th-order diffracted light 80 by the light receiving portions 50 i to 50 l of the photodetector 50, and the light diffracted by the first region 101 of the transparent electrode 100 is the first 1 The light diffracted by the light receiving portions 50m to 50p of the photodetector 50 as the next diffracted light 81 and diffracted by the second region 102 of the transparent electrode 100 is the light receiving portions 50q to 50t of the light detector 50 as the second first diffracted light 82. , And the light diffracted by the third region 103 of the transparent electrode 100 is detected as the third first-order diffracted light 83 by the light receiving portions 50e to 50h of the photodetector 50 (see FIG. 2).

  FIG. 7 is a diagram for explaining the behavior of liquid crystal molecules in each region of the transparent electrode.

  FIG. 7A shows a cross section of the first region 101. In the first region 101 of the transparent electrode 100, a diffraction pattern is formed by a strip-shaped pattern having a predetermined width and arranged in a plurality of pitches s1 along the alignment direction A. Here, when a predetermined potential difference is generated between the transparent electrode 100 and the transparent counter electrode 32, the liquid crystal molecules 37a, 37b, and 37c are aligned along the alignment direction A as shown in FIG. The long needle-like liquid crystal molecules behave gradually.

  FIG. 7B shows a phase difference distribution 91 formed by the first region 101 of the transparent electrode 100 shown in FIG. By forming the phase difference distribution 91 as shown in FIG. 7B, the diffraction grating corresponding to the phase difference distribution 91 as shown in FIG. 7B is formed in the first region 101. This produces the same effect as the above, and exerts a diffractive action on the light passing through the region.

  FIG. 7C shows a cross section of the second region 102. In the second region 102 of the transparent electrode 100, a diffraction pattern is formed by a strip-like pattern having a predetermined width and arranged in a plurality of pitches s2 (s2 <s1) in a direction substantially orthogonal to the alignment direction A. Here, when a predetermined potential difference (the same potential difference as in FIG. 7A) is generated between the transparent electrode 100 and the transparent counter electrode 32, liquid crystal molecules 37d, 37e, and 37f are shown in FIG. 7B. As shown, the long needle-like liquid crystal molecules aligned along the alignment direction A behave gradually.

  FIG. 7D shows a phase difference distribution 92 formed by the second region 102 of the transparent electrode 100 shown in FIG. In the second region 102, since the pitch s2 is narrow, it is affected by the transverse electric field between patterns, and therefore there is a portion where the phase amount does not drop sufficiently between the patterns. Therefore, as shown in the phase difference distribution 92, a distribution in which the difference between the maximum value and the minimum value of the phase amount is smaller than that of the phase difference distribution 91 is generated.

  Therefore, in the second region 102, the same effect as that when the diffraction grating corresponding to the phase difference distribution 92 as shown in FIG. 7D is formed is generated, and the light passing through the region is diffracted. Has an effect.

  FIG. 7E shows a cross section of the third region 103. In the third region 103 of the transparent electrode 100, a diffraction pattern is formed by a band-shaped pattern having a predetermined width and arranged in a plurality of pitches s1 along a direction substantially orthogonal to the alignment direction A. Here, when a predetermined potential difference (the same potential difference as in FIG. 7A) is generated between the transparent electrode 100 and the transparent counter electrode 32, the liquid crystal molecules 37g, 37h, 37i, and 37j in FIG. As shown in FIG. 4, the long needle-like liquid crystal molecules arranged along the alignment direction A gradually behave.

  FIG. 7F shows a phase difference distribution 93 formed by the third region 102 of the transparent electrode 100 shown in FIG. In the third region 103, the pitch s1 is the same as that of the first region 101. However, since the direction of the long needle-like liquid crystal molecules is different, it is affected by the transverse electric field between the patterns, so that the phase between the patterns is sufficient. A portion where the amount does not drop occurs, and as a result, as shown in the phase difference distribution 93, a distribution in which the difference between the maximum value and the minimum value of the phase amount is smaller than the phase difference distribution 91 is generated.

  Therefore, in the third region 103, the same effect as that in which a diffraction grating corresponding to the phase difference distribution 93 as shown in FIG. 7F is formed is generated, and the light passing through the region is diffracted. Has an effect.

  As shown in FIGS. 7A to 7F, if the same potential difference is generated between the transparent electrode 100 and the transparent counter electrode 32 in the first region 101 to the third region 103, the difference is different in each region. This creates a situation where a diffraction grating is generated. That is, even if the same diffraction pattern as the diffraction grating pattern in which the grooves are physically formed is formed on the transparent electrode, it is difficult to obtain diffracted light similar to the diffraction grating.

  FIG. 8 is a diagram illustrating an example of a potential difference applied along one direction of the liquid crystal layer of the liquid crystal optical element and a phase amount corresponding to the potential difference.

  FIG. 8A shows the transparent electrode 100 described with reference to FIG. 6, and FIG. 8B shows diffraction of each region (first region 101 and second region 102) in the BB ′ cross section of FIG. 8A. The potential difference generated between the pattern and the transparent counter electrode 32 is shown, and FIG. 8C shows the phase amount in each region generated in the BB ′ cross section of FIG.

  As shown in FIGS. 7B and 7D, when the same potential difference is generated between the transparent electrode 100 and the transparent counter electrode 32 in the first region 101 and the second region 102 having different pitches, The phase difference distribution that occurs in the region is different. Therefore, in the liquid crystal panel 30, as shown in FIG. 8C, the maximum value and the minimum value of the phase difference distribution generated in the first region 101 are the maximum value and the minimum value of the phase difference distribution generated in the second region 102. As shown in FIG. 8B, the potential difference v1 in the first region 101 and the potential difference v2 in the second region 102 are adjusted so as to be the same as the value (see the phase difference distribution 111) (see the voltage distribution 110). ). Specifically, it was set so that v1 <v2.

  Since the potential difference v1 in the first region 101 and the potential difference v2 in the second region 101 are set as shown in FIG. 8B, in the first region 101 and the second region 102 as shown in FIG. 8C. The liquid crystal panel 30 can be made to function as a diffraction grating having grooves with the same depth.

  FIG. 9 is a diagram illustrating an example of a potential difference applied along the other direction of the liquid crystal layer of the liquid crystal optical element and a phase amount corresponding to the potential difference.

  FIG. 9A shows the transparent electrode 100 described in FIG. 6, and FIG. 9B shows diffraction of each region (first region 101 and third region 103) in the CC ′ cross section of FIG. 9A. The potential difference generated between the pattern and the transparent counter electrode 32 is shown, and FIG. 9C shows the phase amount in each region generated in the CC ′ cross section of FIG.

  As shown in FIGS. 7B and 7F, in the first region 101 and the third region 103 having different diffraction directions with respect to the orientation direction A, the same potential difference between the transparent electrode 100 and the transparent counter electrode 32 is obtained. If this occurs, the phase difference distribution generated in each region will be different. Therefore, in the liquid crystal panel 30, as shown in FIG. 9C, the maximum value and the minimum value of the phase difference distribution generated in the first region 101 are the maximum value and the minimum value of the phase difference distribution generated in the third region 103. As shown in FIG. 9B, the potential difference v1 in the first region 101 and the potential difference v3 in the third region are adjusted so as to be the same as the value (see the phase difference distribution 121) (see the voltage distribution 120). . Specifically, it was set so that v1 <v3.

  Since the potential difference v1 in the first region 101 and the potential difference v3 in the third region are set as shown in FIG. 9B, in the first region 101 and the second region 103 as shown in FIG. 9C. The liquid crystal panel 30 can be made to function as a diffraction grating having grooves with the same depth.

  In the liquid crystal panel 30, as shown in FIG. 8B and FIG. 9B, the liquid crystal driving unit 40 adjusts the potential difference in each region, so the first region 101, the second region 102, and the third region 103. The liquid crystal panel 30 can be made to function as a diffraction grating having grooves of the same depth. That is, by configuring as described above, the liquid crystal panel 30 can be controlled so as to obtain diffracted light similar to a diffraction grating in which grooves are physically formed.

  It should be noted that the number and width of the band-like pattern in the diffraction pattern of the transparent electrode in FIGS. 8 and 9 are examples, and are not limited thereto. Further, the potential difference shown in FIGS. 8B and 9B is configured to be generated by a voltage applied from the liquid crystal driving unit 40 to the transparent electrode 100 and the transparent counter electrode 32.

  As described above, in the optical pickup device 10 shown in FIG. 1, when blue laser light is used, the potential difference in each region is set to the liquid crystal driving unit 40 as shown in FIGS. 8B and 9B. Therefore, the liquid crystal panel 30 functions as a diffractive element, and can diffract the zero-order diffracted light and the three first-order diffracted lights into the photodetector 50 as shown in FIG.

  In the case where a red laser is used, the liquid crystal driving unit 40 has a potential difference of 0 between the transparent electrode 100 and the transparent counter electrode 32 so that no phase amount is generated in all regions of the transparent electrode 100. Control as follows. Therefore, when using a CD and a DVD, the three light beams separated by the diffraction element 23 pass through the liquid crystal panel 30 as they are and irradiate the photodetector 50 as shown in FIG.

  Therefore, by switching the control method of the liquid crystal drive unit 40 by the control signal from the control unit 71, the liquid crystal panel 30 is used as a diffraction element when using a high-density optical recording medium, and as a beam when using a CD or DVD. It can be used as an element (non-diffractive element) that passes through as it is. In addition, since the single liquid crystal panel 30 is used so as to be compatible with high-density optical recording media and CDs or DVDs, the optical pickup device 10 can be reduced in cost and size. It was.

  In the above-described example, the liquid crystal panel 30 is caused to function as a diffraction element that diffracts the first-order diffracted light at an appropriate position when the blue laser light is used. It is also possible to function as a diffraction element. In that case, it is possible to adjust the diffraction change due to the wavelength by controlling the phase difference distribution. That is, the potential difference generated between the transparent electrode 100 and the transparent counter electrode 32 may be adjusted so that a phase difference distribution suitable for the light beam having the wavelength to be used is formed.

  FIG. 10 is a diagram for explaining blazed diffraction.

  FIG. 10A shows an example of the band-like pattern 100a in the first region 101 of the transparent electrode 100 described above, and FIG. 10B shows the phase difference distribution 130 in the first region 101 of the transparent electrode 100. Yes. That is, in the transparent electrode 100 of the liquid crystal panel 30 described above, a binary binary diffraction phase difference distribution is formed by the strip pattern 100a.

  FIG. 10C shows an example of the transparent electrode 200 for performing blazed (sawtooth) diffraction. As shown in FIG. 10 (a), one strip pattern 100a of the transparent electrode 100 has a rectangular shape, but one strip pattern 200a of the transparent electrode 200 for performing blazed (sawtooth) diffraction is , 200a1, 200a2, and 200a3.

  A gradual potential difference is generated between the three parts of each belt-like pattern 200a shown in FIG. 10C and the transparent counter electrode 32, thereby producing a blazed type (see FIG. 10D). Sawtooth type) phase difference distribution 130 'can be generated.

  When the liquid crystal panel 30 is made to function as a diffraction grating having a blazed (sawtooth) phase difference distribution 130 ′, the difference between the maximum phase amount ψ 1 and the minimum phase amount ψ 0 is the wavelength λ of the light beam to be used. If it is 1/2, it is possible to create a situation in which zero-order diffracted light is not generated. Further, it is possible to adjust the light amount of the 0th-order diffracted light by adjusting the difference between the maximum phase amount ψ1 and the minimum phase amount ψ0.

  In FIG. 10C, one strip pattern 200a is subdivided into three parts. However, this is only an example, and it is possible to subdivide into more parts. By subdividing into many parts (e.g., eight divisions), a more accurate blazed (sawtooth) phase difference distribution 130 'can be formed, and no zero-order diffracted light is generated or the zero-order diffracted light is generated. The amount of light can be adjusted more precisely.

  FIG. 11 is a diagram illustrating an example of a phase difference distribution corresponding to the transparent electrode 200 for generating a blazed type (sawtooth type) phase difference distribution.

  The transparent electrode 200 shown in FIG. 11A has a first region 201, a second region 202, and a third region 203, like the transparent electrode 100 shown in FIG. Each of the belt-like patterns included in is subdivided into three parts as shown in FIG. Note that the alignment direction of the liquid crystal and the direction and pitch of the strip pattern in the first region 201, the second region 202, and the third region 203 are the same as those of the transparent electrode 100 shown in FIG. The transparent electrode 200 can be used in the liquid crystal panel 30 instead of the transparent electrode 100.

  FIG. 11B shows a phase difference distribution in each region generated in the BB ′ cross section of FIG. Also in this case, the liquid crystal driving unit 40 adjusts the potential difference in each region so that the difference between the maximum value and the minimum value of the phase amount is the same in the first region 201 and the second region 202. A phase difference distribution 210 is generated. Although not shown, the same applies to the first region 201 and the third region 203.

  FIG. 12 is a diagram showing an example of still another transparent electrode.

  The transparent electrode 300 shown in FIG. 12 also has a first region 301, a second region 302, and a third region 303. The relationship between the direction of the band-shaped pattern of the diffraction pattern in each region and the alignment direction A of the liquid crystal is the same as that of the transparent electrode 100 shown in FIG. However, in the transparent electrode 300 shown in FIG. 12, the pitches of the belt-like patterns in each region are all set to be different. As described above, the transparent electrode of the liquid crystal panel 30 functioning as a diffraction element can appropriately select an optimal diffraction pattern according to the size, arrangement position, and the like of the light detection unit 50.

  In the above-described example, when the transparent electrode is provided with three regions and used as a diffractive element, three first-order diffracted lights are generated. However, only one or two first-order diffracted lights are used as necessary. The region of the transparent electrode may be changed so as to generate 4 or 1st order diffracted light.

  FIG. 13 is a diagram showing a pair of another transparent electrode and a transparent counter electrode.

  FIG. 13A shows a transparent electrode 100 having the same diffraction pattern of the first region 101 to the third region 103 as in FIG. FIG. 13B shows the transparent counter electrode 400 divided into three first to third regions 401 to 403.

  In the example of FIG. 6, the transparent electrode 100 shown in FIG. 6 is divided into three regions, and the applied voltage is changed for each region as shown in FIGS. 8B and 9B. On the other hand, the transparent counter electrode 32 facing the transparent electrode 100 shown in FIG. 6 was a solid electrode, and the same voltage was applied to the whole.

  However, the transparent electrode 100 as shown in FIG. 13A is used to apply the same voltage to all the diffraction patterns in the first region 101 to the third region 103, and FIG. Using the transparent counter electrode 400 as shown, the applied voltage can be changed for each region, and a phase difference distribution similar to the example of FIG. 6 can be generated. That is, the potential difference V1 is between the transparent electrode 100 and the first region 401 of the transparent counter electrode 400, and the potential difference V2 is between the transparent electrode 100 and the second region 402 of the transparent counter electrode 400. A voltage is applied so as to generate a potential difference V3 between the third region 403 of the electrode 400.

  In this way, instead of dividing the diffraction pattern provided on the transparent electrode into a plurality of regions and adjusting the potential difference between the transparent counter electrode for each region, the transparent counter electrode is divided into a plurality of regions, The potential difference with the transparent electrode may be adjusted every time. Rather than dividing a transparent electrode already provided with a diffraction pattern into a plurality of areas, dividing a transparent counter electrode without a diffraction pattern into a plurality of regions is more effective in designing a wiring arrangement for each electrode. There is also an advantage that the degree of freedom increases.

  The division method of the transparent counter electrode region is not limited to the pattern shown in FIG. 13B, and other division methods may be employed.

It is a figure which shows schematic structure of the optical pick-up apparatus which concerns on this invention. It is a figure which shows the photodetector in the case of utilizing a high-density optical recording medium. It is a figure which shows the photodetector 50 in the case of using CD or DVD. It is a figure for demonstrating the drive method of a liquid crystal optical element. 2 is a schematic cross-sectional view of a liquid crystal panel 30. FIG. It is a figure which shows an example of a transparent electrode. It is a figure for demonstrating the behavior of the liquid crystal molecule in each area | region of a transparent electrode. It is a figure which shows an example of the electrical potential difference applied along one direction of the liquid crystal layer of a liquid crystal optical element, and a phase difference distribution corresponding to it. It is a figure which shows an example of the electrical potential difference applied along the other direction of the liquid crystal layer of a liquid crystal optical element, and a phase difference distribution corresponding to it. It is a figure for demonstrating blazed diffraction. It is a figure which shows an example of the phase difference distribution corresponding to the transparent electrode 200 for generating the phase difference distribution of a blazed type (sawtooth type). It is a figure which shows an example of another transparent electrode. It is a figure which shows the pair of another transparent electrode and a transparent counter electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical pick-up apparatus 30 Liquid crystal panel 32 Transparent counter electrode 40 Liquid crystal drive part 45 Liquid crystal optical element 50 Photodetection part 100,200,300 Transparent electrode 100a, 200a Strip pattern 101,201,301 1st area | region 102,202,302 2nd Area 103, 203, 303 Third area

Claims (13)

A liquid crystal layer sandwiched between a pair of transparent substrates, a transparent electrode disposed on one transparent substrate of the pair of transparent substrates and having a diffraction pattern, and disposed on the other transparent substrate of the pair of transparent substrates A liquid crystal panel having a transparent counter electrode,
Diffraction that generates a phase difference distribution in the liquid crystal layer by generating a potential difference between the transparent electrode and the transparent counter electrode, and diffracts the transmitted backward light beam into zero-order light and a plurality of first-order lights. A drive unit that causes the liquid crystal panel to function as an element,
The driving unit divides the diffraction pattern or the transparent counter electrode into a plurality of regions, and generates the phase difference distributions so that the maximum phase amount and the minimum phase amount are substantially the same regardless of the plurality of regions. Adjusting the potential difference between the transparent electrode and the transparent counter electrode for each region of
A liquid crystal optical element characterized by the above. The liquid crystal layer has a predetermined alignment direction, and the transparent electrode or the transparent counter electrode has a first region disposed substantially parallel to the alignment direction of the liquid crystal layer and substantially orthogonal to the alignment direction of the liquid crystal layer. The liquid crystal optical element according to claim 1, wherein the liquid crystal optical element is divided into a plurality of regions with a second region arranged in a direction to be moved. The transparent electrode includes a first region in which the diffraction pattern is arranged at a first pitch, a plurality of regions of the second region in which the diffraction pattern is disposed between said first pitch at a different second pitch The liquid crystal optical element according to claim 1 , which is divided into two parts . The liquid crystal layer has a predetermined alignment direction, and the transparent electrode has a plurality of diffraction patterns arranged in a plurality of different pitches in a direction substantially parallel to or substantially orthogonal to the alignment direction of the liquid crystal layer. The liquid crystal optical element according to claim 1 , which is divided into a plurality of regions. The liquid crystal optical element according to claim 1 , wherein the driving unit generates a blazed phase difference distribution in the liquid crystal panel. A light source that emits a light beam;
A liquid crystal layer sandwiched between a pair of transparent substrates, a transparent electrode disposed on one transparent substrate of the pair of transparent substrates and having a diffraction pattern, and disposed on the other transparent substrate of the pair of transparent substrates A liquid crystal panel having a transparent counter electrode,
A phase difference distribution is generated in the liquid crystal layer by generating a potential difference between the transparent electrode and the transparent counter electrode, and a return light beam of the transmitted light beam is converted into zero-order light and a plurality of primary lights. A drive unit that causes the liquid crystal panel to function as a diffraction element that diffracts the light;
A light detection unit that receives the diffracted light diffracted by the liquid crystal panel, and
The driving unit divides the diffraction pattern or the transparent counter electrode into a plurality of regions, and generates the phase difference distributions so that the maximum phase amount and the minimum phase amount are substantially the same regardless of the plurality of regions. Adjusting the potential difference between the transparent electrode and the transparent counter electrode for each region of
An optical pickup device characterized by that. The liquid crystal layer has a predetermined alignment direction, and the transparent electrode or the transparent counter electrode has a first region disposed substantially parallel to the alignment direction of the liquid crystal layer and substantially orthogonal to the alignment direction of the liquid crystal layer. The optical pickup device according to claim 6 , wherein the optical pickup device is divided into a plurality of regions with a second region arranged in a direction to be moved. The transparent electrode includes a first region in which the diffraction pattern is arranged at a first pitch, a plurality of regions of the second region in which the diffraction pattern is disposed between said first pitch at a different second pitch The optical pickup device according to claim 6 , which is divided into two parts . The liquid crystal layer has a predetermined alignment direction, and the transparent electrode has a plurality of diffraction patterns arranged in a plurality of different pitches in a direction substantially parallel to or substantially orthogonal to the alignment direction of the liquid crystal layer. The optical pickup device according to claim 6 , which is divided into a plurality of regions. The optical pickup device according to claim 6 , wherein the driving unit generates a blazed phase difference distribution in the liquid crystal panel. A first light source that emits a first light beam;
A second light source that emits a second light beam;
A liquid crystal layer sandwiched between a pair of transparent substrates, a transparent electrode disposed on one transparent substrate of the pair of transparent substrates and having a diffraction pattern, and disposed on the other transparent substrate of the pair of transparent substrates A liquid crystal panel having a transparent counter electrode,
A liquid crystal optical element having a drive unit for generating a potential difference between the transparent electrode and the transparent counter electrode;
When the first light beam is emitted from the first light source, the driving unit generates a phase difference distribution in the liquid crystal panel, and a plurality of return light beams of the transmitted first light beam and a plurality of return light beams are transmitted. The liquid crystal layer functions as a diffractive element that diffracts into the first-order light, and when the second light beam is emitted from the second light source, the driving unit causes the liquid crystal layer to function as a non-diffractive element. A switching unit for switching to,
A light detection unit that receives diffracted light diffracted by the liquid crystal panel when the first light beam is emitted from the first light source, and the driving unit includes the diffraction pattern or the transparent counter electrode. And dividing the transparent electrode and the transparent counter electrode for each of the plurality of regions so as to generate a phase difference distribution in which the maximum phase amount and the minimum phase amount are substantially the same regardless of the plurality of regions. Adjust the potential difference between
An optical pickup device characterized by that. The optical pickup device according to claim 11 , wherein when the second light beam is emitted from the second light source, the light detection unit receives the light beam that has passed through the liquid crystal panel functioning as a non-diffractive element. . The optical pickup device according to claim 11 or 12 , wherein the first light beam is a light beam for a high-density optical recording medium, and the second light beam is a light beam for CD or DVD.

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